feat: donglora-cobs workspace crate with 31 spec-compliance tests

Extract COBS encoder/decoder into a separate no_std workspace crate
(crates/donglora-cobs) with comprehensive tests against the Cheshire &
Baker 1999 IEEE/ACM specification and Wikipedia canonical vectors.

Tests cover: empty input, single/multiple zeros, block boundaries at
254/255 bytes, alternating patterns, the Ping regression case (tag 0x00),
round-trip verification, and error cases (truncation, unexpected zeros).

Replace inline cobs_decode() in usb/task.rs with the tested crate.
Replace external cobs dependency with workspace crate.
Fix encoder bug at 254-byte block boundary (spurious trailing code byte).

Cargo.lock

@@ -119,15 +119,6 @@ dependencies = [
  "num-traits",
 ]
 
-[[package]]
-name = "cobs"
-version = "0.3.0"
-source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "0fa961b519f0b462e3a3b4a34b64d119eeaca1d59af726fe450bbba07a9fc0a1"
-dependencies = [
- "thiserror",
-]
-
 [[package]]
 name = "cortex-m"
 version = "0.7.7"
@@ -336,11 +327,11 @@ name = "donglora"
 version = "0.1.0"
 dependencies = [
  "cfg-if",
- "cobs",
  "cortex-m-rt",
  "critical-section",
  "defmt 0.3.100",
  "display-interface",
+ "donglora-cobs",
  "embassy-embedded-hal",
  "embassy-executor",
  "embassy-futures",
@@ -364,6 +355,10 @@ dependencies = [
  "static_cell",
 ]
 
+[[package]]
+name = "donglora-cobs"
+version = "0.1.0"
+
 [[package]]
 name = "embassy-embedded-hal"
 version = "0.2.0"

Cargo.toml

@@ -1,3 +1,6 @@
+[workspace]
+members = [".", "crates/donglora-cobs"]
+
 [package]
 name = "donglora"
 version = "0.1.0"
@@ -21,7 +24,7 @@ embassy-sync = "0.6"
 embassy-time = "0.3"
 embassy-usb = { version = "0.3", features = ["defmt"] }
 embassy-usb-driver = "0.1"
-cobs = { version = "0.3", default-features = false }
+donglora-cobs = { path = "crates/donglora-cobs" }
 heapless = "0.8"
 lora-phy = "3.0"
 static_cell = "2.1"

crates/donglora-cobs/Cargo.toml

@@ -0,0 +1,9 @@
+[package]
+name = "donglora-cobs"
+version = "0.1.0"
+edition = "2021"
+license = "MIT"
+description = "COBS encoder/decoder — no_std, zero-alloc, spec-compliant"
+
+[features]
+default = []

crates/donglora-cobs/src/lib.rs

@@ -0,0 +1,391 @@
+//! COBS (Consistent Overhead Byte Stuffing) encoder and decoder.
+//!
+//! Implements the algorithm from Cheshire & Baker, "Consistent Overhead
+//! Byte Stuffing," IEEE/ACM Transactions on Networking, Vol. 7, No. 2,
+//! April 1999.
+//!
+//! COBS transforms a byte sequence so that `0x00` never appears in the
+//! output, allowing `0x00` to be used as an unambiguous frame delimiter.
+//! Overhead is exactly 1 byte per 254 input bytes (worst case).
+//!
+//! This crate is `no_std` and zero-alloc — suitable for embedded firmware.
+//!
+//! # Examples
+//!
+//! ```
+//! let mut buf = [0u8; 16];
+//!
+//! // Encode
+//! let n = donglora_cobs::encode(&[0x11, 0x00, 0x33], &mut buf).unwrap();
+//! assert_eq!(&buf[..n], &[0x02, 0x11, 0x02, 0x33]);
+//!
+//! // Decode
+//! let mut out = [0u8; 16];
+//! let n = donglora_cobs::decode(&[0x02, 0x11, 0x02, 0x33], &mut out).unwrap();
+//! assert_eq!(&out[..n], &[0x11, 0x00, 0x33]);
+//! ```
+
+#![no_std]
+
+/// Encode `src` into `dest` using COBS. Returns the number of bytes written,
+/// or `None` if `dest` is too small.
+///
+/// The output does NOT include a trailing `0x00` sentinel — the caller
+/// should append it as a frame delimiter.
+pub fn encode(src: &[u8], dest: &mut [u8]) -> Option<usize> {
+    let mut si = 0;
+    let mut di = 0;
+    let mut code_idx = di;
+    let mut need_final_code = true;
+
+    if di >= dest.len() && !src.is_empty() {
+        return None;
+    }
+    // Reserve space for the first code byte.
+    di += 1;
+    let mut code: u8 = 1;
+
+    while si < src.len() {
+        if src[si] == 0x00 {
+            if code_idx >= dest.len() {
+                return None;
+            }
+            dest[code_idx] = code;
+            code_idx = di;
+            if di >= dest.len() {
+                return None;
+            }
+            di += 1;
+            code = 1;
+            si += 1;
+            need_final_code = true;
+        } else {
+            if di >= dest.len() {
+                return None;
+            }
+            dest[di] = src[si];
+            di += 1;
+            si += 1;
+            code += 1;
+            if code == 0xFF {
+                // Block full (254 data bytes) — emit code.
+                if code_idx >= dest.len() {
+                    return None;
+                }
+                dest[code_idx] = code;
+
+                if si < src.len() {
+                    // More input: start a new block.
+                    code_idx = di;
+                    if di >= dest.len() {
+                        return None;
+                    }
+                    di += 1;
+                    code = 1;
+                    need_final_code = true;
+                } else {
+                    // Input exhausted right at the block boundary.
+                    need_final_code = false;
+                }
+            }
+        }
+    }
+
+    if need_final_code {
+        if code_idx >= dest.len() {
+            return None;
+        }
+        dest[code_idx] = code;
+    }
+
+    Some(di)
+}
+
+/// Decode a COBS-encoded buffer. Returns the number of decoded bytes
+/// written to `dest`, or `None` if the input is malformed.
+///
+/// `src` should NOT include the trailing `0x00` frame sentinel — strip
+/// it before calling this function.
+pub fn decode(src: &[u8], dest: &mut [u8]) -> Option<usize> {
+    let mut si = 0;
+    let mut di = 0;
+    while si < src.len() {
+        let code = src[si] as usize;
+        si += 1;
+        if code == 0 {
+            return None; // unexpected zero in COBS data
+        }
+        // Copy `code - 1` data bytes verbatim.
+        for _ in 1..code {
+            if si >= src.len() || di >= dest.len() {
+                return None;
+            }
+            dest[di] = src[si];
+            di += 1;
+            si += 1;
+        }
+        // If code < 0xFF, an implicit zero follows (unless we're at the end).
+        if code < 0xFF && si < src.len() {
+            if di >= dest.len() {
+                return None;
+            }
+            dest[di] = 0;
+            di += 1;
+        }
+    }
+    Some(di)
+}
+
+/// Maximum encoded size for a given source length (excluding sentinel).
+pub const fn max_encoded_len(src_len: usize) -> usize {
+    src_len + (src_len / 254) + 1
+}
+
+#[cfg(test)]
+mod tests {
+    use super::*;
+    extern crate alloc;
+    use alloc::vec;
+    use alloc::vec::Vec;
+
+    fn dec(encoded: &[u8]) -> Option<Vec<u8>> {
+        let mut buf = vec![0u8; 512];
+        decode(encoded, &mut buf).map(|n| buf[..n].to_vec())
+    }
+
+    fn enc(input: &[u8]) -> Option<Vec<u8>> {
+        let mut buf = vec![0u8; max_encoded_len(input.len()) + 1];
+        encode(input, &mut buf).map(|n| buf[..n].to_vec())
+    }
+
+    // ── Wikipedia canonical decode vectors (Cheshire & Baker 1999) ──
+
+    #[test]
+    fn decode_empty() {
+        assert_eq!(dec(&[0x01]), Some(vec![]));
+    }
+
+    #[test]
+    fn decode_single_zero() {
+        assert_eq!(dec(&[0x01, 0x01]), Some(vec![0x00]));
+    }
+
+    #[test]
+    fn decode_two_zeros() {
+        assert_eq!(dec(&[0x01, 0x01, 0x01]), Some(vec![0x00, 0x00]));
+    }
+
+    #[test]
+    fn decode_single_nonzero() {
+        assert_eq!(dec(&[0x02, 0x11]), Some(vec![0x11]));
+    }
+
+    #[test]
+    fn decode_zero_delimited() {
+        assert_eq!(
+            dec(&[0x01, 0x02, 0x11, 0x01]),
+            Some(vec![0x00, 0x11, 0x00])
+        );
+    }
+
+    #[test]
+    fn decode_mixed() {
+        assert_eq!(
+            dec(&[0x03, 0x11, 0x22, 0x02, 0x33]),
+            Some(vec![0x11, 0x22, 0x00, 0x33])
+        );
+    }
+
+    #[test]
+    fn decode_no_zeros() {
+        assert_eq!(
+            dec(&[0x05, 0x11, 0x22, 0x33, 0x44]),
+            Some(vec![0x11, 0x22, 0x33, 0x44])
+        );
+    }
+
+    #[test]
+    fn decode_trailing_zeros() {
+        assert_eq!(
+            dec(&[0x02, 0x11, 0x01, 0x01, 0x01]),
+            Some(vec![0x11, 0x00, 0x00, 0x00])
+        );
+    }
+
+    #[test]
+    fn decode_all_zeros_4() {
+        assert_eq!(
+            dec(&[0x01, 0x01, 0x01, 0x01, 0x01]),
+            Some(vec![0x00, 0x00, 0x00, 0x00])
+        );
+    }
+
+    #[test]
+    fn decode_all_ff_4() {
+        assert_eq!(
+            dec(&[0x05, 0xFF, 0xFF, 0xFF, 0xFF]),
+            Some(vec![0xFF, 0xFF, 0xFF, 0xFF])
+        );
+    }
+
+    #[test]
+    fn decode_alternating() {
+        assert_eq!(
+            dec(&[0x01, 0x02, 0x01, 0x02, 0x02, 0x02, 0x03]),
+            Some(vec![0x00, 0x01, 0x00, 0x02, 0x00, 0x03])
+        );
+    }
+
+    // ── Block boundary tests (254/255 bytes) ────────────────────
+
+    #[test]
+    fn decode_254_nonzero() {
+        let input: Vec<u8> = (1..=254).map(|i| i as u8).collect();
+        let mut encoded = vec![0xFF];
+        encoded.extend(1u8..=254);
+        assert_eq!(dec(&encoded), Some(input));
+    }
+
+    #[test]
+    fn decode_255_nonzero_split() {
+        let input: Vec<u8> = (1..=255).map(|i| i as u8).collect();
+        let mut encoded = vec![0xFF];
+        encoded.extend(1u8..=254);
+        encoded.push(0x02);
+        encoded.push(0xFF);
+        assert_eq!(dec(&encoded), Some(input));
+    }
+
+    // ── Ping regression (tag byte 0x00 was stripped by old decoder) ──
+
+    #[test]
+    fn decode_ping_tag_zero() {
+        assert_eq!(dec(&[0x01, 0x01]), Some(vec![0x00]));
+    }
+
+    // ── Error cases ─────────────────────────────────────────────
+
+    #[test]
+    fn decode_unexpected_zero() {
+        assert_eq!(dec(&[0x00]), None);
+    }
+
+    #[test]
+    fn decode_truncated() {
+        assert_eq!(dec(&[0x04, 0x11]), None);
+    }
+
+    #[test]
+    fn decode_empty_input() {
+        assert_eq!(dec(&[]), Some(vec![]));
+    }
+
+    // ── Encode tests ────────────────────────────────────────────
+
+    #[test]
+    fn encode_empty() {
+        assert_eq!(enc(&[]), Some(vec![0x01]));
+    }
+
+    #[test]
+    fn encode_single_zero() {
+        assert_eq!(enc(&[0x00]), Some(vec![0x01, 0x01]));
+    }
+
+    #[test]
+    fn encode_single_nonzero() {
+        assert_eq!(enc(&[0x11]), Some(vec![0x02, 0x11]));
+    }
+
+    #[test]
+    fn encode_mixed() {
+        assert_eq!(
+            enc(&[0x11, 0x22, 0x00, 0x33]),
+            Some(vec![0x03, 0x11, 0x22, 0x02, 0x33])
+        );
+    }
+
+    #[test]
+    fn encode_no_zeros() {
+        assert_eq!(
+            enc(&[0x11, 0x22, 0x33, 0x44]),
+            Some(vec![0x05, 0x11, 0x22, 0x33, 0x44])
+        );
+    }
+
+    #[test]
+    fn encode_trailing_zeros() {
+        assert_eq!(
+            enc(&[0x11, 0x00, 0x00, 0x00]),
+            Some(vec![0x02, 0x11, 0x01, 0x01, 0x01])
+        );
+    }
+
+    #[test]
+    fn encode_254_nonzero() {
+        let input: Vec<u8> = (1..=254).map(|i| i as u8).collect();
+        let mut expected = vec![0xFF];
+        expected.extend(1u8..=254);
+        assert_eq!(enc(&input), Some(expected));
+    }
+
+    // ── Round-trip tests ────────────────────────────────────────
+
+    #[test]
+    fn roundtrip_empty() {
+        roundtrip(&[]);
+    }
+
+    #[test]
+    fn roundtrip_single_zero() {
+        roundtrip(&[0x00]);
+    }
+
+    #[test]
+    fn roundtrip_ping() {
+        roundtrip(&[0x00]); // Ping command = tag 0
+    }
+
+    #[test]
+    fn roundtrip_mixed() {
+        roundtrip(&[0x11, 0x22, 0x00, 0x33, 0x00, 0x00, 0x44]);
+    }
+
+    #[test]
+    fn roundtrip_254_nonzero() {
+        let data: Vec<u8> = (1..=254).map(|i| i as u8).collect();
+        roundtrip(&data);
+    }
+
+    #[test]
+    fn roundtrip_255_nonzero() {
+        let data: Vec<u8> = (0..255).map(|i| (i + 1) as u8).collect();
+        roundtrip(&data);
+    }
+
+    #[test]
+    fn roundtrip_256_with_zeros() {
+        let mut data = vec![0u8; 256];
+        for (i, b) in data.iter_mut().enumerate() {
+            *b = i as u8; // 0x00, 0x01, ..., 0xFF
+        }
+        roundtrip(&data);
+    }
+
+    fn roundtrip(input: &[u8]) {
+        let mut enc_buf = vec![0u8; max_encoded_len(input.len()) + 1];
+        let enc_len = encode(input, &mut enc_buf).expect("encode failed");
+        let encoded = &enc_buf[..enc_len];
+
+        // Verify no zero bytes in encoded output.
+        assert!(
+            !encoded.contains(&0x00),
+            "encoded output contains 0x00: {:?}",
+            encoded
+        );
+
+        let mut dec_buf = vec![0u8; input.len() + 1];
+        let dec_len = decode(encoded, &mut dec_buf).expect("decode failed");
+        assert_eq!(&dec_buf[..dec_len], input, "round-trip mismatch");
+    }
+}

src/usb/task.rs

@@ -124,7 +124,7 @@ async fn protocol_loop<'d, D: embassy_usb_driver::Driver<'d>>(
                         if frame_len > 0 {
                             let mut decode_buf = [0u8; MAX_FRAME];
                             if let Some(decoded_len) =
-                                cobs_decode(&frame_buf[..frame_len], &mut decode_buf)
+                                donglora_cobs::decode(&frame_buf[..frame_len], &mut decode_buf)
                             {
                                 if let Some(cmd) = Command::from_bytes(&decode_buf[..decoded_len]) {
                                     route_command(
@@ -147,7 +147,8 @@ async fn protocol_loop<'d, D: embassy_usb_driver::Driver<'d>>(
             Either3::Second(response) => {
                 // Serialize response to fixed-size LE bytes, then COBS encode
                 let raw_len = response.write_to(&mut write_buf);
-                let encoded_len = cobs::encode(&write_buf[..raw_len], &mut cobs_encode_buf);
+                let encoded_len = donglora_cobs::encode(&write_buf[..raw_len], &mut cobs_encode_buf)
+                    .unwrap_or(0);
                 // Append 0x00 sentinel
                 if encoded_len < cobs_encode_buf.len() {
                     cobs_encode_buf[encoded_len] = 0x00;
@@ -209,32 +210,135 @@ async fn route_command(
     }
 }
 
-/// Decode a COBS-encoded buffer (without the trailing 0x00 sentinel).
-/// Returns the number of decoded bytes, or None on error.
-fn cobs_decode(src: &[u8], dest: &mut [u8]) -> Option<usize> {
-    let mut si = 0;
-    let mut di = 0;
-    while si < src.len() {
-        let code = src[si] as usize;
-        si += 1;
-        if code == 0 {
-            return None; // unexpected zero in COBS data
-        }
-        for _ in 1..code {
-            if si >= src.len() || di >= dest.len() {
-                return None;
-            }
-            dest[di] = src[si];
-            di += 1;
-            si += 1;
-        }
-        if code < 0xFF && si < src.len() {
-            if di >= dest.len() {
-                return None;
-            }
-            dest[di] = 0;
-            di += 1;
-        }
+
+// ── COBS compliance tests (IEEE/ACM Cheshire & Baker 1999) ──────
+
+#[cfg(test)]
+mod tests {
+    use super::cobs_decode;
+
+    fn decode(encoded: &[u8]) -> Option<Vec<u8>> {
+        let mut buf = vec![0u8; 512];
+        cobs_decode(encoded, &mut buf).map(|n| buf[..n].to_vec())
+    }
+
+    // Wikipedia canonical vectors
+    #[test]
+    fn empty_input() {
+        assert_eq!(decode(&[0x01]), Some(vec![]));
+    }
+
+    #[test]
+    fn single_zero() {
+        assert_eq!(decode(&[0x01, 0x01]), Some(vec![0x00]));
+    }
+
+    #[test]
+    fn two_zeros() {
+        assert_eq!(decode(&[0x01, 0x01, 0x01]), Some(vec![0x00, 0x00]));
+    }
+
+    #[test]
+    fn single_nonzero() {
+        assert_eq!(decode(&[0x02, 0x11]), Some(vec![0x11]));
+    }
+
+    #[test]
+    fn zero_delimited() {
+        assert_eq!(
+            decode(&[0x01, 0x02, 0x11, 0x01]),
+            Some(vec![0x00, 0x11, 0x00])
+        );
+    }
+
+    #[test]
+    fn mixed_with_zero() {
+        assert_eq!(
+            decode(&[0x03, 0x11, 0x22, 0x02, 0x33]),
+            Some(vec![0x11, 0x22, 0x00, 0x33])
+        );
+    }
+
+    #[test]
+    fn no_zeros() {
+        assert_eq!(
+            decode(&[0x05, 0x11, 0x22, 0x33, 0x44]),
+            Some(vec![0x11, 0x22, 0x33, 0x44])
+        );
+    }
+
+    #[test]
+    fn nonzero_then_trailing_zeros() {
+        assert_eq!(
+            decode(&[0x02, 0x11, 0x01, 0x01, 0x01]),
+            Some(vec![0x11, 0x00, 0x00, 0x00])
+        );
+    }
+
+    #[test]
+    fn all_zeros_4() {
+        assert_eq!(
+            decode(&[0x01, 0x01, 0x01, 0x01, 0x01]),
+            Some(vec![0x00, 0x00, 0x00, 0x00])
+        );
+    }
+
+    #[test]
+    fn all_ff_4() {
+        assert_eq!(
+            decode(&[0x05, 0xFF, 0xFF, 0xFF, 0xFF]),
+            Some(vec![0xFF, 0xFF, 0xFF, 0xFF])
+        );
+    }
+
+    #[test]
+    fn alternating_zero_nonzero() {
+        assert_eq!(
+            decode(&[0x01, 0x02, 0x01, 0x02, 0x02, 0x02, 0x03]),
+            Some(vec![0x00, 0x01, 0x00, 0x02, 0x00, 0x03])
+        );
+    }
+
+    // The Ping case that caught the original bug
+    #[test]
+    fn ping_command_tag_zero() {
+        assert_eq!(decode(&[0x01, 0x01]), Some(vec![0x00]));
+    }
+
+    // 254-byte block boundary (code 0xFF = 254 data bytes, no implicit zero)
+    #[test]
+    fn block_254_nonzero() {
+        let input: Vec<u8> = (1..=254).collect();
+        let mut encoded = vec![0xFF];
+        encoded.extend(1u8..=254);
+        assert_eq!(decode(&encoded), Some(input));
+    }
+
+    // 255 non-zero bytes: first 254 as one block, then 1 leftover
+    #[test]
+    fn block_255_nonzero() {
+        let input: Vec<u8> = (1..=255).map(|i| i as u8).collect();
+        let mut encoded = vec![0xFF];
+        encoded.extend(1u8..=254);
+        encoded.push(0x02); // code for 1 data byte
+        encoded.push(0xFF); // the 255th byte
+        assert_eq!(decode(&encoded), Some(input));
+    }
+
+    // Error cases
+    #[test]
+    fn unexpected_zero_in_data() {
+        assert_eq!(decode(&[0x00]), None);
+    }
+
+    #[test]
+    fn truncated_input() {
+        // Code says 3 data bytes follow, but only 1 available
+        assert_eq!(decode(&[0x04, 0x11]), None);
+    }
+
+    #[test]
+    fn empty_encoded() {
+        assert_eq!(decode(&[]), Some(vec![]));
     }
-    Some(di)
 }